Different types of arc discharge lamps are known, each comprising a sealed discharge vessel and at least two electrodes projecting into a sealed discharge space within the discharge vessel. An arc discharge lamp generates light from an electrical arc ignited between the electrodes. According to the type of lamp, there may be different components provided within the discharge vessel, in particular a filling gas at a specified filling pressure and other ingredients such metal halides or, optionally, mercury.
Electrical power is supplied to the electrodes by a driver circuit. This may include a high voltage pulse for igniting a discharge between the electrodes. Typically, a discharge created will start as a glow discharge and quickly transit into an arc discharge.
For example, in an automotive HID lamp, i. e. a lamp intended for use in a headlamp of an automobile, electrical power is supplied to the electrodes as an alternating current. In the run-up period, after the electrical arc has been successfully established, known automotive HID lamps, e. g. with a nominal power of 35 W, are first operated by limiting the current to a maximum value. In a later stage of the run-up period, the lamp may be operated in a power control mode, according to a power curve, decreasing over a predetermined time from an initial higher power value to the nominal power value. Upon transition into steady-state operation, the electrical power supplied to the lamp as an alternating current, preferably as a square wave, is controlled at the nominal power of the lamp.
US 2009/0230870 describes an electronic ballast for high intensity discharge lamps. Formation of an arc is controlled by ignition control, glow-to-arc transition current control and initial arc development current control. The arc thus formed is stabilized in arc stabilization current control, followed by lamp power control during normal operation. During this period, an alternating current is supplied first at a higher switching frequency during an initial arc development stage and later at a constant, lower frequency during arc stabilization and normal operation. Before switching from the higher to the lower frequency, there is an increase of the voltage, lamp current and operating frequency.